1. Technical Field
The present invention relates to electronic circuits in general, and in particular to noise suppression circuits. Still more particularly, the present invention relates to noise suppression circuits for suppressing above-supply and below-ground noises.
2. Description of the Prior Art
As electronic circuits continue to reduce in size, metallurgical limitations begin to have more influence on line-to-line interconnect coupling. At a minimum, line-to-line interconnect coupling can increase effective load capacitance if a signal line is switching when a neighboring net is concurrently switching in an opposite direction from the signal line. As a result, there will be an increase in switching time for the signal line.
Furthermore, line-to-line interconnect coupling can also cause noise. Generally speaking, noise can bounce in one or more of the following four distinct directions: above ground, below ground, above power supply, and below power supply. Noises that are above ground and below power supply can cause false switching events if the coupling effects cause a signal to cross the switching threshold of a given destination circuit. On the other hand, noises that are below ground and above power supply can cause a loss of state in some types of latch circuits.
Thus, it is desirable to eliminate those effects, such as noises, that are caused by the line-to-line interconnect coupling. The present invention provides a noise suppression circuit for suppressing noises that are above power supply and a noise suppression circuit for suppressing noises that are below ground.